Typical actuators have poor torque density (by volume or weight) partly because they require extra hardware (bearings, levers, pivots . . . ) to support the main elements (motor, transmission).
For example, a linear actuator (motor and ball-screw) requires a lever and bearings to convert the linear motion into rotational motion. Although highly energy-efficient, this arrangement is typically bulky and heavy.
Another example is the rotational actuator (motor and in-axis transmission) requires an output stage bearing to support loads. This bearing is typically located axially on the actuator or on the outer diameter, which can significantly increase the size and weight of the actuator.
Furthermore, robotic actuators require protection for over torque conditions. The solution to this typically consists in a slip clutch or other similar device. Consequently, commercial versions of such devices are cumbersome and heavy.
Accordingly, there is a need for a lighter and more compact actuator.